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914World.com _ 914World Garage _ Amazing
Posted by: Hawktel Sep 17 2005, 10:56 PM
So the new Impalla that chevy has released has a option for a 330 HP V8 with 28 highway fuel consumption.
Thats amazing. Just amazing. I wonder how far fuel efficency can be pushed?
Posted by: Elliot Cannon Sep 17 2005, 11:07 PM
28 miles per gallon at what speed? 55? 60?
Elliot
Posted by: Hammy Sep 17 2005, 11:07 PM
Had to be a typo 
How is that possible? 
Posted by: Hammy Sep 17 2005, 11:14 PM
From Chevy site
| QUOTE |
| ...That’s because only four of the eight cylinders are activated during some driving conditions to increase your fuel economy – up to an estimated MPG 28 highway.1 When you need full power, the other four cylinders are reactivated. |
I know another car had this feature before... I forget which one. I'm pretty sure it was German. I'm thinking Mercedes?
Posted by: Twystd1 Sep 17 2005, 11:23 PM
My bro has a 2003 Vette with the z06 package and about 400 ponies to play with.
he typically gets about 30 MPG from LA to vegas...
IF he is mellow and stays between 70 and 80 MPH. And keeps it in 6th.
These are REAL numbers. Cause I was with him..!!!!!!!!!
Then again.. if he stands on it and gets into a race for a 100 or so miles.. The MPG goes down to ZIP...........
Twystd1
Posted by: DonTraver Sep 17 2005, 11:24 PM
Cadilac's (sp)
Posted by: Travis Neff Sep 17 2005, 11:25 PM
Ayup, my Dad has a the last year WS6 Trans Am with a 6 speed. Drove from Seattle to Phoenix and got very high 20's. Damn thing in 6th gear at 80MPH - the car is just barely braking idle
Posted by: redshift Sep 18 2005, 12:20 AM
Simple: The stated EPA milage is an F'ING LIE.
Just read a report, stated can be as much as 35% higher than actual, depending on condition, and the hybrids were the worst liars. 
M
Posted by: sean_v8_914 Sep 18 2005, 02:10 AM
I just drove a new Vette on a mini AX style track this thursday. 400 HP and 28 MPG, no gas guzzler tax. since wind resistence is non linear and the Vette has a small frontal cross section, 28-30 mpg is beleivable. it also has that feature that shuts down cylinders based on demand.
at 3150lbs, it's slower than my 914 
hadta brag 
Posted by: Hammy Sep 18 2005, 02:18 AM
How does the vette handle?
Posted by: TimT Sep 18 2005, 05:42 AM
Im sure the vette handles pretty well..
the assholes on pelican trashed a guy for posting about the new corvette.
I think as mentioned above, that cadillac had an engine that would lose cylinders to run more efficiently
It was badged 8-6-4 or something, it didnt work that well
Posted by: Gint Sep 18 2005, 07:12 AM
| QUOTE (TimT @ Sep 18 2005, 05:42 AM) |
| Im sure the vette handles pretty well.. the assholes on pelican trashed a guy for posting about the new corvette. I think as mentioned above, that cadillac had an engine that would lose cylinders to run more efficiently It was badged 8-6-4 or something, it didnt work that well |
That was it. The Cadillac V8-6-4. I knew a lady that had one back in the day. The technology of the time couldn't make it work extremely well. There are now several manufacturers doing cylinder shutdown technology. I'm sure today it works better than it did in the early 80's. What the hell eh? Whatever works.
Personally, I'd love a new Vette and I don't care what anybody has to say about it. At least it's not a Miata.
Posted by: Dr Evil Sep 18 2005, 07:50 AM
I believe it is called "variable displacement." My friend was telling me that the original design had issues with the pistons, crank, and rods getting goofed up when someone would want more power and they were switching from 4cyl to 8cyl. Supposedly, the new design has features that protect the engine from this.
Posted by: seanery Sep 18 2005, 08:16 AM
Chrysler has been doing the multiple displacement thing for a couple years with the Hemi in it's cars and now trucks. It's a 4 cylinder then an 8 when needed.
Posted by: Pugbug Sep 18 2005, 12:14 PM
They are all liars!...This from Consumers Reports.
Fuel economy
Why you're not getting the mpg you expect
For years, automakers have been criticized for producing vehicles that get so-so gas mileage. But as gas prices climb and consumers seek more miles per gallon, it turns out that fuel economy is much worse than it appears--50 percent less on some models, a new Consumer Reports analysis reveals.
Drivers who track their own fuel economy have long known that their results seldom match the gas mileage claimed by the Environmental Protection Agency on new-car stickers. Our study, based on years of real-world road tests over thousands of miles, quantifies the problem across a wide swath of makes and models.
We compared the claimed EPA fuel economy with the mileage per gallon we measured for 303 cars and trucks for model-years 2000 to 2006. Our selection represents a good cross-section of mainstream, high-volume vehicles. We looked at city, highway, and overall mpg.
Highlights of our study:
• Shortfalls in mpg occurred in 90 percent of vehicles we tested and included most makes and models.
• The largest discrepancy between claimed and actual mpg involved city driving. Some models we tested fell short of claimed city mpg by 35 to 50 percent.
• Hybrids, whose selling point is fuel thriftiness, had some of the biggest disparities, with fuel economy averaging 19 mpg below the EPA city rating.
• The EPA ratings are the result of 1970s-era test assumptions that don't account for how people drive today. Automakers also test prototype vehicles that can yield better mileage than a consumer could get.
• Despite federal certification, it appears that U.S. vehicle fleets, all cars and light trucks produced in one model year, don't meet government fuel-economy standards. For example, fleet mpg for 2003-model-year vehicles we studied was overstated by 30 percent.
Posted by: redshift Sep 18 2005, 12:24 PM
Stop-and-Go numbers in my city, are higher than 90% of other citys, because my city MAKES YOU STOP at EVERY light..
It's a rip off.
M
Posted by: Headrage Sep 18 2005, 12:31 PM
| QUOTE (TimT @ Sep 18 2005, 04:42 AM) |
| It was badged 8-6-4 or something, it didnt work that well |
Mid '70's Eldorado I think. I had a friend that had one.
It sucked...
I'm sure the technology is better now though.
Posted by: bd1308 Sep 18 2005, 12:31 PM
how does the system work? are the fuel injectors shut off, both injectors and plugs....
are cylinders shut off in diagonal order, or a different order depending on firing order and setup....
Posted by: bd1308 Sep 18 2005, 12:32 PM
| QUOTE (redshift @ Sep 18 2005, 12:24 PM) |
| Stop-and-Go numbers in my city, are higher than 90% of other citys, because my city MAKES YOU STOP at EVERY light.. It's a rip off. M |
here, the lights are only suggestion....
red means stop if you want
yellow means hello
and green means go really fast through the light.
Posted by: snflupigus Sep 18 2005, 12:41 PM
Imagine, displacement on demand, variable compression, and variable valve timing all in one, then add lithium ion regen braking hybrid with a tiny fuel cell just in case you run out of gas!!!! 1000mpg LOL!!!
http://www.saabnet.com/tsn/press/000318.html
I've got a much better idea.... spend some money to make gas F'n CHEAPER AGAIN by building some damn refineries in the US and find an environmentally friendly way tapping Alaska!!!! (which i will argue COULD be done). I also argue that the increased productivity and freedom of travel and shipping in the US would increase GDP and tax revenue and that increase could go right back into the whole environmentally friendly ideas.
[waiting for all the hippy tree huggers to now attack me]
LOL
Posted by: snflupigus Sep 18 2005, 12:50 PM
| QUOTE (bd1308 @ Sep 18 2005, 11:32 AM) |
| [/QUOTE] here, the lights are only suggestion.... red means stop if you want yellow means hello and green means go really fast through the light. |
LOL - here too... we actually have signs that say special redlight reinforcement area. I couldnt believe my eyes when i saw those in phoenix. Those signs dont exist in nebraska or iowa... it blew my mind that signs have to be put up to try and keep people from running red lights... HAVE SOME GOD DAMN COMMON COURTESY people!!! Next there will be rifle towers with gaurds on every corner shoot out your tires for running reds. naziland usa
Posted by: anthony Sep 18 2005, 12:55 PM
How is it that manufacturers cheat by such a large margin on the epa tests. I know they drive the cars like a granny - and of course nobody in real life does that.
My '94 VW has actually gotten better mileage than the 23/30 EPA certification. I get 26mpg on average and 32mpg on 75-80mph straight freeway trips.
Posted by: Pugbug Sep 18 2005, 02:30 PM
And the fuel economy winner is........The Pac car at 5385 Kilometers per liter!
http://www.ethz.ch/news/ethupdate/2005/050625_2/index_EN
Attached image(s)
Posted by: snflupigus Sep 18 2005, 03:31 PM
i used to get about 25mpg average on interstate trips from denver to omaha in my 305 throttle body injected 3600lb automatic 92 camaro. On the interstate i could go 360 miles to a tank. in the city i would get something like 230 miles out of a tank. roughly 14 gallon tank.
255lb ft, 170hp 5L v8.... the 70's technology designed ecm has a "lean mode" function where if the speed and throttle position stay at certain range over 60mph for so long it leans out the fuel to safe but very lean. Most new cars have that as well and they are much more aerodynamic.
I think i remember being taught while working for my families gm dealership that it only takes something like 8hp to keep the vette going at 60mph once it gets there. i might be off there though.
anyway, if they could get 25mpg out of a 92 camaro, 35-40mpg would seem more than feasible out of a v8 today tuning for something more like 300lb ft and 250hp. Make it a v6 and i think 50mpg with 200hp,200lb/ft should be the standard... but instead our cars have gotten heavier and more powerful. instead of lighter and more efficient.
the 914 starting to look pretty good again for a daily driver LOL
Posted by: bd1308 Sep 18 2005, 05:17 PM
on your 914 comment, I couldn't agree more.
The longer I own the 914, the more I enjoy driving it!
Posted by: dmenche914 Sep 18 2005, 05:22 PM
The 914 is light enough, so it does not need a ton of power to still be fun (heck it handles so well it be fun with a lawn mower engine).
What we need is better milage, a more effiecient type four motor, or a water cooled replacement that is light, super efficient, and not over powered (at expense of economy)
A lower ratio 5th gear would be helpful with the right engine to obtain incredeble highway MPG I would assume 50 mpg highway woudl be possible in a so modified 914.
Try to shave a few pounds off the stock 914, add a smaller but new effiecient engine, select a very low ratio overdrive top gear to match the new engine for best economy,a dn you could end up with a rear winner.
Lucky most of our 914's are smog exempt in Californazia so that we can make energy saving modifications legally at last (Sorry 1976 owners, Shwartznegger screwed you, you got to stay stock)
Posted by: groot Sep 19 2005, 05:46 AM
The manufacturers don't cheat on the sticker numbers. The EPA does the testing and certification.... and I agree it's flawed. They have a very specific city loop and highway loop and it doesn't come close to real life.
There have been talks about revising this silly EPA standard, but what would the customers do if all of a sudden they went into a showroom and saw the fuel economy sticker to be 20-40% lower than it was on the same model than it was last year?
Posted by: roundboy914 Sep 19 2005, 07:56 AM
not for nothing, but i think the HP rating was 303, not 330. Still not bad at all.
Posted by: andys Sep 19 2005, 09:50 AM
Though I've only put four tankfulls' since I bought it, my '05 Toyota Tacoma truck bested at 17.5 MPG combined. Rating is 18/22. I expect it will get slightly better as it loosens-up, but it still falls short for now. My previous old '83 Toyota SR5 truck with 279K miles did 24 MPG combined all day long.
Andys
Posted by: snflupigus Sep 19 2005, 10:10 AM
at least comparitively they are useful... one truck/car at 18mpg epa rating will get better gas mileage as another truck/car w/ epa rating of 16mpg.
right?
Posted by: jniemeier Sep 19 2005, 01:04 PM
I'm new to the group, but you're on a topic I know something about.
Warning: long boring post to follow: Read only if you want to know more than absoutely necessary about cylinder deactivation.
(I was the Engineering Supervisor for the Delphi Valve Train group when we developed the cylinder deactivation system used by GM.)
The old Cadillac system used an electric rotary actuator on top of the rocker arms. We found a '82 Seville with a V8-6-4 when we started working on the new system in '99, and it was still working fine. Must have been the only one left. Putting electrical connections under the valve covers is generally a bad idea. Someone mentioned the Mercedes. Their V8 and V12 were the first of the 'modern' systems (I think in '99), and was very complicated. Big surprise. It's very tough to switch off the valves in an overhead cam engine. It has a very expensive, high pressure valve asm. You've only got the rockers to do it in, and it's hard to get the right oil circuits to your hydraulic actuators (inside the rockers!). Honda have also done it this way. You need a pivot shaft running down the length of the head so the rockers stay in perfect alignment and for the oil to run in. ($)
The new systems from GM (Displacement on Demand) and Chrysler (Multiple Displacement System) are almost identical. They (we) are doing the switching in the Roller Hydraulic Valve Lifters of pushrod engines. Much cheaper. There's enough space there to add locking pins and when hydraulically unlocked to absorb the cam lift without moving the pushrod. Ford would be doing the same, but they seem to have forgotten how to make pushrod engines, so they are out of the party for now. Chrysler's are made by INA (Germany); GM's by Delphi and Eaton. (Yes, legal wrangling has ensued, but let's not talk about that)
Operationally, it switches off the exhaust first, then the intake of every other cylinder as you go throught the firing order. The lifter has to be on the cam's "base circle" to allow the locking pins to move. That means inside cylinders on one bank and outsides on the other. Hence, the motor stays even firing. The engine mounts are bi-state (!), and are electrically switched to a different natural frequency in sync with the motor switching. It is all done within two engine cycles, and no, you can't feel it. GM's calibrators can't even feel it. They wire up an LED on the dash for reference. There is an electrically actuated hydraulic control valve for each cylinder that fire in sequence driven by the ECM and the cam position sensor. Think high speed: elec signal, solenoid movement, oil pressure buildup, locking pin movement... all in 10 milliseconds, and repeatable over the full range of oil temps. Hint: changing your oil regularly is a good idea.
As to economy, as always, it depends. I'm talking full size trucks and TrailBlazers here. The overall real world average they figure to be 8%. Might not sound too huge, but to a car company, that's a big number. In suburban driving, ~45ish and lot's of light loads, it could be over 20%. On the other hand, I heard the calibration guys say once that about 75mph is where the "road load" power required prevents it from going into deac. So, I doubt the heavier versions of the trucks are deac'g much on the highway. I guess running a 6 or 7 thousand pound truck on 4 cylinders isn't too easy. Our job was to just get them turned off and on, not make it more powerful in 4cyl mode. As mentioned, not it's also in the Impala SS. I didn't think they were doing the Corvette, but maybe so. It's also possible to do a V6, although the useable range of loads is a bit narrower. To even-fire a V6 in 3 cylinder mode, you need to deac one whole bank. And, yes, it's been done on a 4 cylinder by a research firm, but... well, let's see how the V8's are accepted.
Concerns? Oil puddling on top of the valve guides, and then getting sucked in when the cylinder suddenly "re-acts". GM's trucks periodically switch back to 8 cyl even if not required to prevent this. The fuel injectors are off of course, but the spark is still on. No need to add the complexity of switching it on and off.
Sorry for the long post, but engineers never know when to shut up.
Jim N.
'73 2.0
Posted by: jd74914 Sep 19 2005, 01:30 PM
very interesting. thanks
Posted by: groot Sep 19 2005, 01:46 PM
Great post, Jim!!!
I hadn't read how the cylinders are being deactivated.
So, you still have pumping loses, correct? ... which would explain the 8% improvement.
Posted by: 914efi Sep 19 2005, 01:58 PM
What happened to Saab's variable compression engine?
Posted by: BIGKAT_83 Sep 19 2005, 02:09 PM
Great post Jim..............
Thanks for the info 
Posted by: Rotary'14 Sep 19 2005, 04:04 PM
IIRC the EPA accepts data provided from the manufacturer to "vouch" for the fuel economy. It's up to the manufacturers to be ready for an audit if it ever comes.
All fuel economy tests regardless of vehicle type are done under standard conditions. The test (FTP75) is a modified version of the original test that was put together in 1975. The test was generated by data logging the driving habits of a "typical" driver in the Los Angeles area during 1970s rush hour street driving. All test are done with the A/C off, and the heater in full cool position.
In the 8+ years of performing this test for manufacturers, I can tell you that small displacement engines will have a larger discrepency between EPA and real world fuel economy figures. Most people drive in the real world with the A/C on, or the windows down. The FTP75 test has a max speed that is less than 55 MPH, and on the highway version of the test the max speed is ~62 MPH. Most people nowadays don't drive this slow. I'm sure some of these factors explain the mileage discrepancy.
-Rob
Posted by: jniemeier Sep 20 2005, 04:08 PM
This followup will be short, I promise.
Reduction in "pumping losses" is why Deac improves economy. By pumping losses I mean the work required to pull down on intake against the restriction of the throttle blade. When in 4 cyl mode, a deac engine has it's throttle blade further open than it would in 8 cyl mode at the same speed-load point. Think: working harder on the remaining four cylinders. Further open means air flows in easier, i.e. less losses.
If you mean the frictional losses of the piston going up and down with both valves closed all the time, yes of course that is an unavoidable loss of efficiency, but it's not that bad, cuz the work required to compress the air is recovered when it expands. You only lose the friction, which isn't terrible with a warm engine and the low tension rings they use now-a-days.
Saab's Variable Compression engine is no doubt still around, and still in development. (Did you hear about the one that sparked from the plug to the top of the piston? Those Swedes!) These things take years. I've also seen one from FEV, a Euro engine design company in their Detroit office. It's a steep uphill challenge: added complexity means lower reliability, and more variables means tougher to meet emissions reg's, which is the hardest aspect of designing an engine. And when a new engine line costs many hundreds of millions, they tend to be a conservative bunch. Believe me. Very conservative. On the other hand, engines are now extremely reliable when you think about it.
OK, not short, but let's call this one medium. See you around. Good questions.
Jim N
'73 2.0
Posted by: Mueller Sep 20 2005, 04:20 PM
thanks Jim 
Posted by: phantom914 Sep 20 2005, 04:35 PM
Jim N,
I have a dumb question which I ask because I don't feel like thinking right now and because, well, I'm dumb. What would be the problem of just shutting off the injectors for particular cylinders and leaving the valvetrain operating normally? Wouldn't there still be a gain in economy?
Oh, and isn't part of the increased efficiency due to the fact that the remaining cylinders are operating with a greater charge density? I was under the impression that a denser charge burns more efficiently.
Andrew
Posted by: ewdysar Sep 21 2005, 03:41 PM
As long as we're on a rant topic... OK we're not but 
Toyota says they've got 9 (wow 9!) models that get 30+MPG. So what! And those are EPA figures!
In real life, my '58 bug (with the ragtop and windows usually open) got 30 MPG all the time. 47 years later, technology has done what? For a closer example, my 1990 Geo Metro, which cost $7k (it was the luxury model), got 50+MPG on all but 2 tanks of gas over 130K miles (when the mileage dropped to 44 MPG, I knew there was something terribly wrong) The Metro fit 4 adults and could cruise over the Grapevine at 65 with the airconditioning on. That car actually got better mileage with the AC running than AC off with the windows down. Under any reasonable analysis, high MPG versions of any cars offered today will not cover their premium price while gas is under $6 a gallon.
We're being screwed by Big Oil, Big Auto, Big Government 
and we're collectively letting them. 
Even if everyone that I come in contact with understands and agrees, we are completely overwhelmed by the rest of the populace. 
We are sinking in a sea of mediocrity, I see more lemmings than sheep from where I sit.
Man I hate this, I feel better when I don't think about these things. But I've got a plan... 
Don't worry, be happy!
End of rant...
Eric
Posted by: jniemeier Sep 21 2005, 06:51 PM
First, Eric- I agree completely. We could cut the oil consumption of cars and light trucks in half with today's technology. i.e. Double fuel economy. No sweat. But we can't do it while driving Tahoe's, Durango, Expeditions, and Land Bruisers... For me, step one is diesel. Instant 30% improvement with no sacrifice or downside for Joe American. Europe is now 50%+, US is <1%. I can tell you diesels are finally coming to the States. The fuel will be 30ppm sulfer I think in '06 or was it '07. That allows the diesel catalysts to live. Get ready for a gradual 20 year roll-in to reach 40 or 50% penetration. I don't know anything special about fuel cells, but I'm optimistic they will eventually make them economical. They've only scratched the surface compared to the millions and millions of man-hours invested in getting IC engines to work well.
Andrew- good guestion. You're making think, which has it's pro's and con's most days. Wish I could draw you a P-V Diagram. (Pressure vs Volume as a four stroke completes one cycle) Pulling the connectors on four injectors would certainly make things worse. The throttle blade would be open a bit more, as on a deac engine, but the non-firing cylinders would be wasting more energy pulling air in against the manifold vacuum and then pushing it out against the exhaust back pressure. It's a loser in both directions. These losses would be worse than the slight gain in the firing cylinders.
If you've heard it said that an engine is just a big air pump- well, that may be true but it's sure an inefficient one cuz the first thing you come to is a nearly closed off throttle valve. At highway cruise it's only open 10%. 90% blocked off, which is proven by the huge vacuum in the manifold. My 914 pulled 14.5psi vacuum at idle when I tested it this fall. That's a measure of how inefficient a motor is, not the opposite. One of the reasons diesels are more efficient is because they don't need a throttle valve, so there's no vacuum in the manifold. i.e., it's very easy for the pistions to suck in the next gulp of air. So, controlling a gas engine by throttling the air (both at the throttle valve and at the intake valves- don't forget) is inherently worse than controlling a diesel by the amount of fuel injected.
Charge density helps but it's not more efficient, it just has more air and fuel cuz it's denser. That's why intercoolers help. Cool air is denser (more) air, to which it's easy to add a smidge of extra fuel, and so get more power. Remember, you need to stay very close to the optimal 14.7:1 ratio. Burn rate and burn completion is mostly due to fuel atomization (droplet size), and local air/fuel ratio (how homogenious is it in there really?) and the degree of turbulence created by the intake velocity and direction and the shape of the upwardly rushing piston against the chamber shape.
Time to put the cookie-munchers to bed.
Jim N.
'73 2.0
Posted by: phantom914 Sep 21 2005, 11:12 PM
Jim,
Makes sense. If an engine had individual drive-by-wire throttles, would it be simpler to switch those out (closed) rather than the valves? And what if there were similar butterfly or other type of valves on the exhaust side. Wouldn't it be less complex than deactivating the valvetrain? Or if not less complex, would it work? I think it wouldn't work as well since the butterfly valves woudn't seal as well as a closed cylinder-head valve. I am just curious whether you think it would work at all since that would seem to address the pumping loss issues you mention. Don't think that I was thinking of trying it.....
.....this year... ...
I do still think that (maybe?) a fuller cylinder will burn more efficiently. It is harder to ignite and sustain ignition in a partially filled cylinder compared to a more fully filled one. I don't know the exact mechanism(s), but the pressure developed before and after ignition, heat generated by combustion and heat rate lost to cylinder walls etc affect ease of starting/sustaining combustion and also energy output/efficiency. Some of these factors would be affected by the amount of cylinder filling, wouldn't they?
Also, a car will get better mileage with higher gearing. Which of these factors are significant: 1) less frictional loss due to engine turning fewer revs over a given distance2) less pumping loss due to higher throttle opening 3) increased efficiency due to greater cylinder filling 4) any thing I didn't mention.
Is that too many questions? (oops, that was another one)
Andrew
Posted by: jniemeier Sep 23 2005, 07:49 PM
We call them ETC's: Electronic Throttle Control, and no, that won't work. For one, you can't put an ETC into a 500deg C exhaust stream. Well, you could, but it wouldn't live long. Why do you think this would work better? Doing it in the valvetrain is the closest to the combustion chamber we're trying to control and by far the most mechanically simple (engineers would say, "elegant") solution. There's no need to think up anything else.
Individual throttles implies you're using individual intake runners. Very expensive and won't fit for a V type engine. V engines like plenum's and a single throttle cuz it helps even out the flow balance to the cylinders, fits better, and of course is lots cheaper. Racing engines may have seperate runners, but keep in mind they are optimized around a very narrow rpm band.
Cylinder filling: I don't think you caught what I wrote before. You need to seperate the idea of quality of combustion from the amount of mixture in there. To have acceptable emissions, you need to keep the mixture at 14.7 to 1 air/fuel ratio. Period. After that, the AMOUNT of 14.7:1 mixture we get in there is the thing that directly controls the torque that cylinder makes. At Wide Open Throttle (WOT), less restriction to air flowing in, more mixture in the cylinder, max torque. At idle, tons of restriction past the throttle, little mixture inside, low torque. In both cases, the mixture is always 14.7 to 1. It takes a while to digest that fact. So, things like the ease of initiating the burn, and the combustion 'efficiency' are the same in both cases. The power generated is drastically different of course, so the heat loss to the wall is different, sure, but the efficiency is the same. Engines are most efficient at WOT not because they burn better, but because they don't waste work pulling air past the nearly closed throttle at low loads.
Answer to paragraph #3: Number 1 and 2 are both good, although I think number 1 is the easiest and likely the larger improvement, at least for big V8's. With a 914 engine pushing the car at 70 mph, you can't be lowering the revs too much can you? But, when Chevy was trying to avoid the gas guzzler tax on the Vette inspite of increasing hp to 400 (and now 500!), they went to gearing that left it turning what, 1600 at 70? Something like that. IF you have the torque, that's the easiest way to go. By now, I hope you agree that Number 3, increased filling, is simply a method to increase torque, not improve efficiency, BUT, you can use your increased torque to drive taller gearing, and THAT is option Number 1, the best option. So, 3 is just an enabler for 1. Got it?
Now, since you're such an inquisitive guy, here's my advice I hope you take on board: Go to a used book store (or probably Amazon) and buy a copy of "Internal Combustion Engines and Air Pollution" by Obert. That's the one used in most engineering schools and is the all time classic. Every engine designer in the country has a copy in his office. Read the whole thing. It's actually not that hard to read. I'm sure you will get a ton out of it.
Jim N.
Posted by: stock93 Sep 24 2005, 08:32 AM
Jim N,
Check out BMW's N73 6.0L V 12. They are the only gas engine I have seen that has direct injection in the actual cylinder like a diesel. This engine also has Valvetronic which is something else to check out.
John
Posted by: jniemeier Sep 24 2005, 09:03 AM
Yes, it's an amazing engine. Not the first though.
DIG was intro'd by Mitsubishi about 10 years ago, although it wasn't new then. The '55 Mercedes SLR had mechanical DIG.
The Valvetronic system came out on BMW's European 318 in about '99. They have been gradually increased the volume of manufacture.
Jim N.
Posted by: snflupigus Sep 24 2005, 01:44 PM
Thinking of the whole torque = good for economy with the right gearing.
so why did my near 4k lb 92 camaro camaro rev at only something like 14-1500 at 60mph and idled at 5-600rpm. with 170hp and 255lb/ft, an auto and 2.73 rear end it got fairly! good gas mileage even with a terribly slow ecm and not so accurate throttle body injection system.... I also am told it has the lowest lift cam ever put into a gm engine. wouldnt that cause more restriction and worse economy that a larger cam tuned betted at the ecm..
ahhhh. the LO3 never ceased to confuse me.. LOL
then thinking of an ex's neon idling at what 2k rpm and cruising the 60mph at 3500rpm! i hated that car but it did get better mileage than my camaro. lighter and smaller engine is the answer there i guess. I need to start reading up on all of this.
Jim, you've obviously studdied and worked in the field for years and years - what schools etc would you recomend to pursue your career? I hear Colorado has an advanced engine theory program...
Posted by: Carl Sep 25 2005, 01:20 AM
Very interesting information, Jim.
For a long time I've wondered when we'll have the technology to build an electronically controlled valve train so that cams would be eliminated. To do this would require a strong, lightweight, temperature resistant gating device that would control cylinder intake and exhaust. The engine controller then could choose the most efficient timing for opening and duration for the engine loads. I imagine conventional solenoids are too slow to activate conventional valves this way but is there anything in the pipeline for this concept?
Thanks,
Carl
Posted by: snflupigus Sep 25 2005, 02:48 AM
The selenoids would also have to operate at certain rates of opening and closing too.... can they do that? Arent most selenoids essentially on or off, open or closed. Wouldnt it be tough to have one selenoid open really fast and then really slow wouldnt it? Or would it be easy with varying electrical signal to them.
Posted by: J P Stein Sep 25 2005, 06:37 AM
| QUOTE (jniemeier @ Sep 24 2005, 07:03 AM) |
| The '55 Mercedes SLR had mechanical DIG. |
As did the 1938 DB601 series engines.
That Foker was in a Messerschmitt..
Posted by: kwales Sep 25 2005, 09:41 AM
There has been a lot of work beign done on solenoid actuated valve trains and quite a few patents filed. Back when I did patent work, I would review the Official Gazette from the patent office and would take a side jaunt into the auto engine section (200-250?).
Having done work with solenoids, there are a lot of problems. One, the more you use one, the hotter it gets. The hotter it gets, the less efficient it becomes. You lose force big time when hot (80%?).
Next problem is the way they work. Solenoids create magnetism and magnetic strength depends on distance. If it is a linear solenoid, the force produced is weakest at the start and gets stronger and stronger as the armature approaches the end of the stroke. Not what you really need for overcoming a valve spring so you would tend to use a really big solenoid to get the force you need initially. Big solenoids need big power and produce big heat which reduces the force and then you need a bigger solenoid and.... round and round you go.
I was hoping that some of the room temperature superconductors could be made cost effective and they would possibly be the solution.
Ken
Posted by: snflupigus Sep 25 2005, 01:49 PM
so how do fuel injectors continue working? The fuel cools them off right? I know with the large throttle body injection type injectors the throttle body itself would get cold to the touch on a hot motor sometimes so i guess the injectors themselves would have been cool from the whole fuel atomizing etc..
Posted by: jniemeier Sep 25 2005, 08:51 PM
Someone asked about schools. I have no special advice about that. Find a school that has a solid Mechanical Engineering program. Most state universities do. Specialization comes in your masters program, should you go that route, and most people advise going to a different school for your masters anyway. Getting a degree is to teach you to think, and what get's you in a company's door. Actual useful knowledge starts when you get to work. That said, it's a good idea to pay attention when they teach IC Engines by Obert. (See above) I took it from a German, ex-VW engine guy whom we were legitimately afraid of.
Electric Valve Trains: Now there's a subject we could all debate for weeks. Basic benefit: Changing the duration of the lift event on the fly. Think of the motion of today's cam and spring driven valves. Cam design programs calculate four derivatives: (you paid attention in math class, right?) displacement, velocity, acceleration, and jerk. Even the jerk has to be smooth, if that makes sense. There's a whole lot more to it than lift and duration. Ok, fine. Chances of replicating this motion with an electrical solenoid? Zero. But do we need this gradual start - fast lift - gradual stop type motion? Well, if you want to keep from fracturing valve stems, you sure need to gradually close the valve. The solenoid guys call this "soft landing", and I understand there are patents for that via reversing the current at just the right moment. How do you know when the right moment is? You now need a valve position sensor. And it better be a darn fast one considering how fast the valve is moving much less the extremely nasty environment (see earlier posts). If you can do the soft landing, how much juice will it take to run the solenoids? Last I read, a couple research firms said they could do it with 1.5 kilowatts for a 16v four cylinder. Not terrible, but still too much, and I don't think it's been demonstrated either, although EMVT cars have certainly been driven around. (I'm sorry I don't know right off how much power it takes to drive a 4 cylinder's cam- but keep in mind that when the follower is on the back side of the profile, the spring is returning energy to the system not consuming it.) After we figure out lift profile, soft landing, position feedback, and power consumption, we still must face reliability of elec connections, packaging it to fit, noise (very important), lubrication, cost of the solenoids, cost of the control electronics, packaging of the control electronics, manufacturability and of course durability. It's a huge challenge, but what's new? There are a lot of bright guys in research companies who thought they could do it. Notice I've switched to past tense. I think full electric valve train is a pretty cold trail. One caveat though: HCCI combustion (Homogeneous Charge Compression Ignition) could be a huge efficiency improvement, but may require VT control like electric valves. If you want to know about HCCI, you'll have to look it up. I can't explain it very well. Think of controlling a gas engine like a diesel. Extremely tough, although I think this one will ultimately succede.
The fully variable valvetrain that's in production of course is BMW's Valvetronic. It changes lift and duration at the same time. We designed a system that did this also, but we could never get it cheap enough to sell it. I guess BMW has a different view of the value equation for new technologies. Interesting question: how much valve lift does it take to idle a 4 cyl engine? 0.3mm or even a bit less. That's amazing. And you can do it at 500 rpm or so, which saves a bunch of fuel. Turns out cars spend a lot of time idling.
There are a bunch of systems that change lift in two and even three steps. Most famous is Honda's VTEC. They have at least 6 variations of it in production, including on the new 3 liter V6 that does high and low lift and cylinder deac in the same engine. That is fantastic, and no doubt comes close to the benefit of Valvetronic for a lot less money. The Mitsubishi MIVEC system can do three steps and has been around for a while. Porsche have a two step system on the Turbo which is made by INA of Germany. Then of course there's cam phasing. That's old news, and on most cars these days.
The system that I've just read that IS going to enter production is Fiat's Electro Hydraulic VT. They sometimes call it UniAir. Electric solenoids open a high pressure oil circuit which has an actuator to open the valve. This sounds like a good idea, but the hydraulic fluid was always a challenge. The viscosity change due to temperature was a killer. Evidently FIAT have solved that problem. They will use it on a diesel (lower redline) starting next year or so. UniAir can do variable duration and lift by basically truncating the lift profile when it's had enough by dumping the oil through a relief valve. Should be great if it works. I actually met Dr Petronio, the father of UniAir once. (I was selling, but he wasn't buying!) He had been working on it for years at that time, and you could just tell that by-God he was not going to give up. Sometimes, even in a corporation the size of FIAT-GM Powertrain (they've since split up) it boils down to one very tenacious guy. In fact, I think it almost always does. That's interesting, eh?
Oh, and don't bother trying to dream up other "gates" or types of valves besides poppet valves, like the spherical rotating ones you read about. Talk about patents- in valve types, everything has been tried before. Nothing will seal combustion pressure like an inward opening poppet valve. No matter what system creates the opening and closing motion, today's poppet valves will always be used in piston engines. And don't even get me started on ported two strokes.
Pop quiz: How does a Ferrari valve get a larger lift profile than the what's ground into their cam?
Now, if I write any more you guys are going to have to start passing the hat. I'm going to bed.
Jim N.
'73 2.0 with a nicely lashed, single return spring, pushrod and rocker arm mechanical valve train that I can fix and adjust in my garage.
Posted by: Carl Sep 25 2005, 09:44 PM
Jim,
Thanks for such a thorough response to my question. I appreciate your explanation of these systems and I guess we won't be seeing camless engines anytime soon.
Carl
Posted by: 914GT Sep 25 2005, 09:59 PM
| QUOTE (snflupigus @ Sep 25 2005, 01:48 AM) |
| The selenoids would also have to operate at certain rates of opening and closing too.... can they do that? Arent most selenoids essentially on or off, open or closed. Wouldnt it be tough to have one selenoid open really fast and then really slow wouldnt it? Or would it be easy with varying electrical signal to them. |
In our robotics storage systems at my work we pulse-width-modulate (PWM) the current to various solenoids in order to control their actuation speed, as well as significantly lower their holding current. Whether or not these same methods would work in automotive valve actuators I do not know.
Posted by: brp914 Sep 25 2005, 10:25 PM
ok, you headed me off at the pass with rotating valves - always wondered about that. How about on the fly oxygen enrichment. Combine that on a turbo direct inj. diesel. O2 is paramagnetic...higher molecular wt. than N2...different ionization energy...something. Well, if it's a stupid idea, so be it. If it makes money, I get 0.000001% of profit (or 1 beer, whichever is less). If you try it and it doesn't work, its all your fault.
btw, you're not qualified to adjust your valves.
Posted by: Dr. Roger Sep 25 2005, 11:13 PM
Hi Jim,
Nice to read a chat from someone who's got some alternative engine know how.
I built a Grubb/Pogue prototype on a mini bike engine a couple of years ago and now that gas prices are skyrocketing my thoughts are going back to Pogue's fuel system.
I've always been facinated with Pogue and Otto engines. What are your thoughts on them?
As far as i'm concerned, there is no contest as to the efficency and cleanliness of a fuel vapor (warm or cold) as opposed to fual atomization system (injected or not). Oh yes, and cooler running. =-) Oh, and less fuel oil dilution. Oh, and zero carbon build up...
Roger
Posted by: jniemeier Sep 26 2005, 07:19 PM
This is the first thing Google found about Pogue, and it seems about right.
http://www.mikebrownsolutions.com/fish3.htm
Jim N.
Posted by: MattR Sep 26 2005, 08:16 PM
| QUOTE (jniemeier @ Sep 26 2005, 05:19 PM) |
| Cam design programs calculate four derivatives: (you paid attention in math class, right?) displacement, velocity, acceleration, and jerk. |
Jim,
Your posts are very interesting. Ive read them all once and Im going to read through them again. Having just taken a quarter of thermodynamics, all this stuff is freash on my mind. My impression on the Fish carburator; its not based on science, because it obviously fails, but its based on skepticism of science.
I do have a question about this statement though. You say 4 derivatives, now what are these derivatives? My math skills are sufficient (6 quarters of college calc.) but not necessarily proficient, but I obviously dont have much experience with this knowledge being a 3rd year mech e student. Displacement is dVolume/dt, velocity is dDisplacement/dt, acceleration is dVelocity/dt. Does this mean jerk is dAcceleration/dt? If so, wont having a cam profile of x^5 mean jerk is always smooth? And any exponential value of 4 or less will have 0 jerk? Im not sure how Im communicating my ideas, but I dont have a piece of paper in front of me.
Posted by: phantom914 Sep 26 2005, 11:00 PM
Jim,
Thanks for answering my questions (and for shooting down my hair-brained ideas 
).
I will shut up about cylinder filling promoting a more efficient burn. I thought something I read sometime ago implied this and I thought it was a great opportunity to ask the question since we have somebody (you) with first-hand knowledge. 
And I didn't mean to imply that butterfly valves would be better in the sense that a manufacturer should do it that way, else it would have been done that way. As a mental exercise, I wondered if it would work at all and if a crazy person wanted to try it on his own, I thought that it was more feasible to implement homebrew cylinder deactivation with butterfly valves. No sophisticated throttle position control would be needed. Since this is a fully open/fully closed situation, I envisioned solenoids and butterfly valves and only on the intake runners and exhaust primary tubes of the cylinders that would be deactivated. The intake runners would still be connected to a plenum and there would be only one throttle body, with the extra butterly valves only being used to deactivate the cylinders, not throttle control. Would it work? Again, just for fun. 
It's great to have genuine expertise (you again ) here rather than the all too common speculation presented as fact.
Thanks for the book recommendation. I'll look for it.
Andrew
Posted by: phantom914 Sep 26 2005, 11:15 PM
| QUOTE (MattR @ Sep 26 2005, 06:16 PM) | ||
Jim, Your posts are very interesting. Ive read them all once and Im going to read through them again. Having just taken a quarter of thermodynamics, all this stuff is freash on my mind. My impression on the Fish carburator; its not based on science, because it obviously fails, but its based on skepticism of science. I do have a question about this statement though. You say 4 derivatives, now what are these derivatives? My math skills are sufficient (6 quarters of college calc.) but not necessarily proficient, but I obviously dont have much experience with this knowledge being a 3rd year mech e student. Displacement is dVolume/dt, velocity is dDisplacement/dt, acceleration is dVelocity/dt. Does this mean jerk is dAcceleration/dt? If so, wont having a cam profile of x^5 mean jerk is always smooth? And any exponential value of 4 or less will have 0 jerk? Im not sure how Im communicating my ideas, but I dont have a piece of paper in front of me. |
Matt,
On the derivatives, you are on the right track. First, I'm not sure, but I think Jim may have meant third derivative? I will explain a little based on that assumption, but if he meant fourth derivative, you can carry this example just one step further. The third derivative is also called jounce (at least when referring to a vehicle's wheel motion). I believe you want to have the third derivative be zero in the case of suspension movement to have a perceived good ride. In other words, acceleration should be constant. If the third derivative is not zero, that means acceleration is changing wrt time and that is what supposedly is the most objectionable sensation in a car's ride. I hope Jim can clarify his statements regarding the number of derivatives.
Oh, just noticed. There is a slight mistake in your statement. Regarding motion, displacement has nothing to do with volume, it relates to motion (distance travelled). So displacement is 'x'. Velocity is dx/dt. Acceleration is dv/dt and jounce is da/dt. And to go back to your statement, if the diplacement as a function of time is third order, the third derivative (jounce) is constant. If it is second order, jounce is zero. If it is fourth order or higher, jounce would vary over time.
My interpretation of what defines good or bad jounce and how it affects ride quality is only based on something I was told, so it may not be completely correct, but the rest of my explanation should be accurate.
But I'm just guessing.
Andrew
Posted by: Dr. Roger Sep 26 2005, 11:37 PM
| QUOTE (jniemeier @ Sep 26 2005, 06:19 PM) |
| This is the first thing Google found about Pogue, and it seems about right. http://www.mikebrownsolutions.com/fish3.htm Jim N. |
That's alright Jim,
IMHO, I feel that when there is so much engineering and so little progress regarding MPG numbers, that indicates the need for a fundamental paradigm change in the way engines operate. But that is just me.
I did make a little 4 stroke motor idle using my own bubbler device. Crude is an understatement as to it's engineering but I know it works.
I even brought a friend and his mom to witness just in case of doubters. =-)
Keep up the good work and hope to see pics of that 2.0.
Roger
just another "out of the box" thinker, amateur engineer, designer, builder, 914 owner.
PS. A little better data on the Pogue. See Data B.
http://www.himacresearch.com/books/crisis1.html
Posted by: bare 1 Sep 26 2005, 11:51 PM
Could one of you kind intelligent gentleman please explain to me why my rear wheel bearing died before I even got the brake rotor completely on . please Pretty please. Thanks In the aaaaaaaaaaiiiiiiiii what did I do wrong post. I'm just a simple fellow. And frustrated. and perhaps a bit crude for you enginners.
Posted by: MattR Sep 27 2005, 12:19 AM
| QUOTE (phantom914 @ Sep 26 2005, 09:15 PM) | ||||
Matt, On the derivatives, you are on the right track. First, I'm not sure, but I think Jim may have meant third derivative? I will explain a little based on that assumption, but if he meant fourth derivative, you can carry this example just one step further. The third derivative is also called jounce (at least when referring to a vehicle's wheel motion). I believe you want to have the third derivative be a constant in the case of suspension movement to have a perceived good ride. In other words, acceleration should be to cx^1 (c is a constant). If the third derivative is not constant, that means acceleration is changing wrt time and that is what supposedly is the most objectionable sensation in a car's ride. I would guess it is similar in the case of valve movement that Jim describes. Oh, just noticed. There is a slight mistake in your statement. Regarding motion, displacement has nothing to do with volume, it relates to motion (distance travelled). So displacement is 'x'. Velocity is dx/dt. Acceleration is dv/dt and jounce is da/dt. And to go back to your statement, if the diplacement as a function of time is third order, the third derivative is constant. If it is second order, jounce is zero. If displacement is fourth order or higher, jounce varies with time which I think is a bad thing. But I'm just guessing. Andrew |
Okay Andrew. That clears some things up. Im not quite sure why I wrote the displacement and volume statement. Rereading that, you're totally right. I'm still have a bit of trouble visualizing jounce and jerk. I'll break out the good book when Im not so tired (RCVD).
Posted by: phantom914 Sep 27 2005, 12:33 AM
Matt,
In your sleep deprived state, you confused the idea of displacement with volume because you were thinking of engine displacement.
Think of jounce like this. If you were experiencing a constant acceleration (zero jounce), you would feel a contant force being exerted against you. If the acceleration were changing over time (non-zero jounce), the force you felt being exerted on you would change over time.
Again, this may have nothing to do with what Jim was saying, but is only to explain some things about derivatives, at least up to the third derivative.
Andrew
Posted by: snflupigus Sep 27 2005, 02:30 AM
while we're on efficiency and alternatives in combustion engine design...
wrench going in....
quasiturbine?
http://www.quasiturbine.com/ETheoryEngineProblematic.htm
Posted by: jniemeier Sep 27 2005, 07:45 PM
OK, you guys are already finding my mistakes... which I'm willing to admit I make quite a few of. Including ending sentences with prepositions.
First, yes, jerk is the third derivative of cam lift, isn't it? You got me there.
Andrew, very interesting to read about constant accel in wheel control motion being required for a good feeling ride. Leave it to the engineers to make a mathmatical equation for feeling quesy. I've got as many questions about suspension design as you guys have about engines, so maybe we can go in that direction next.
Back to cams: acceleration is definately not constant in a typical cam profile, so jerk is non-zero. I've seen production profiles where there's a sharp bend in the accel curve, therefore a step or discontinuity in the jerk curve. A cam like that could have acceptable durability, but it puts a heck of a load spike into the valve train. And, I should have explained before that the reason we calc all those crazy derivatives is to predict the forces in the valve train and therefore the stress at various critical points in the components. It's tough to sum it up in a sentence, but let's try: smooth jerk curves lead to better fatigue life, which allows the parts to survive the most stress, and we'll put our stress capability to good use by snapping the valve open as quickly, but smoothly as possible. To fill the cylinder with the most mixture possible (filling! (for max torque)) you would want to be as close as possible to the ideal, which would be a rectangular lift profile (instant open and close) but since that would give infinite stress (generally bad), we do the best we can. How quick you can pop open the valve depends on the weakest link (lowest load capability) in the chain (valve train).
No one bit on the Ferrari question, so here's another: In a typical pushrod V8 at redline, how much force exists in the valve train? Like if you could grab the pushrod, how much force would it be pushing upward with? (Another trailing preposition!! Urgh)
Matt, where are you going to school? Any engine classes yet? What sort of field do you want to work in?
Jim N, who wishes he knew how to make quotes appear in those cool green boxes...
Posted by: Mueller Sep 27 2005, 08:16 PM
| QUOTE |
| Pop quiz: How does a Ferrari valve get a larger lift profile than the what's ground into their cam? |
at least for one motor, they a few different profiles on one lobe, the cam shaft moved back and forth to increase/decrease the lift..more than likely not what you are talking about
pushrod force? 3.5K#'s???
Posted by: Dr. Roger Sep 27 2005, 09:09 PM
| QUOTE (Mueller @ Sep 27 2005, 07:16 PM) | ||
at least for one motor, they a few different profiles on one lobe, the cam shaft moved back and forth to increase/decrease the lift..more than likely not what you are talking about pushrod force? 3.5K#'s??? |
Ferrari uses something like a V-tec engine. V-TEC stands for Variable Valve Timing and Lift Electronic Control.
The Vtec solenoid pumps fluid into a small pinion, which engages a different lifter which makes 2 valves work off of 1 cam lobe instead of each valve having it's own lobe..In essense in a DOHC(Dual Overhead Cam) car you get the benefits of 4 camshafts.. 2 different intake cams and 2 different exhaust cams (due to the profile change.
| QUOTE |
| From Honda - i-VTEC The 'intelligent' VTEC Since the creation of the revolutionary VTEC system, Honda has advanced engine efficiency even further, with the invention of i-VTEC. The 'i' denotes an even more 'intelligent' power-plant. This evolution of Honda's renowned VTEC technology employs Variable Timing Control (VTC), which allows the engine to vary its intake camshaft phasing. This means that the intake ports are able to open and close earlier or later, providing precisely the right amount of fuel and air at exactly the right time for driving requirements. The result is better fuel economy and low emissions because the system virtually precludes the exhaust of unburned fuel. Now that's intelligent! i-VTEC is found in Honda's CR-V, Integra, Odyssey, Accord and Accord Euro cars. |
Is this what you were thinking about Jim?
Posted by: messix Sep 27 2005, 09:18 PM
the push rod would have as much force as it would take to bend or break the push rod, lifter or cam/ cam drive.
Posted by: phantom914 Sep 27 2005, 10:35 PM
| QUOTE (jniemeier @ Sep 27 2005, 05:45 PM) |
| ................. Jim N, who wishes he knew how to make quotes appear in those cool green boxes... |
You mean like this? Just go to the post you want to quote and click the "quote" button in the upper right hand corner.
Andrew
Posted by: phantom914 Sep 27 2005, 10:43 PM
| QUOTE (jniemeier @ Sep 27 2005, 05:45 PM) |
| .......No one bit on the Ferrari question, so here's another: In a typical pushrod V8 at redline, how much force exists in the valve train? Like if you could grab the pushrod, how much force would it be pushing upward with? (Another trailing preposition!! Urgh) .......................... |
I don't know. If there is valve float, there might be very little force (zero?) as the pushrod "falls off" the back side of the lobe? When opening the valve, I'm sure there is a lot.
that's a slightly longer way of saying "I don't know". 
Andrew
Posted by: snflupigus Sep 27 2005, 11:22 PM
"Chromoly 4130 is a tough material with a tensile strength that varies from 140,000 psi up to 240,000 psi depending on the heat treatment. For all out racing applications such as Top Fuel, Pro Stock, Pro Modified, Blown Alcohol, NASCAR Cup racing, marine racing and tractor pulling, 4140 chromoly tubing can provide up to 275,000 psi of tensile strength. "
from
http://www.aa1car.com/library/2004/eb30431.htm
Posted by: jniemeier Sep 28 2005, 09:26 PM
Ok, here's my quiz answers, although you may find someone else who says something quite different. YMMV as they say.
Before I can go on though, just how the heck does one pronounce "snflupigus"? Not only do I not have any cool green boxes, I don't have a cool pic on the left, or a cool signoff stamp, or,... I'm going to have to quite writing posts and figure out how the site works a bit more.
Ferrari have a system called "Ballistic Lift". We call it "Toss and Catch". I imagine it started on race motors, but I think even the 360 uses it. I'll tell my one cool Ferrari story below. Anyhow, they have this cam profile that works normally at "low" speeds, but at a certain point, the lift curve overcomes the springs and it literally throws the cam follower off the cam and therefore gets the valve open further (I think) and longer (I'm sure) than what is ground into the profile. Then the tricky part is that it "catches" the follower again in such a way as to not put a huge impact load into the valve train. Kinda like valve float on purpose, but without the impending-doom part.
Our lifter engineer says that a Chevy small block at 6000rpm or so puts about 5000 N (1100 lbf) through it's pushrods. Considering that this happens about every 20 milliseonds, I think it's pretty impressive. (The 4130 stress numbers were great. I don't know how hard the production pushrods are- but I can tell you that you can bend them if you try hard enough.) Andrew, you're right, when a valve floats, the force in the pushrod would be a lot less, only the spring load. Keep in mind, that the inertial loads in the valve train get to be much larger than the valve spring load once you get some revs. Anyhow, I can say that designing a hydraulic lifter that doesn't leak down too much under 5000N loads requires some pretty tight tolerances. Like if you pick up the inner part and hold it in your hand a few seconds, it will no longer fit in the outer part. Roger, good info about VTEC. The "i" version is one of the newer derivatives. What they call VTC, we call Cam Phasing. Pretty common, but in combo with all their other VT controls, they must have pretty good oil pump capacity to run it all. Most engines barely have enough pump capacity to run the phasers at idle, which is definately required.
What else... Quick Ferrari Story: In about '98 or so, I was working out of our European office (Luxembourg) and we went to Maranello to sell evap canisters to Ferrari for their US market cars. Hey, somebody has to do these things, you know. Before the meeting, (since I'm a big F1 fan) I suggest lunch at Restorante Montana, which is a famous little place right alongside the test track in Fiorano. Sure enough while we're eating our pasta, Micheal walks in with his Indian trainer/dietician guy and they shake hands with all the old Italian men and go into the back to eat. As we're getting our bill paid, they walk back through, so naturally we followed them out. Just as we get to the end of the sidewalk, Micheal comes wheeling around the little driveway in a Alfa 164 and comes within a meter of driving over my foot! He gives a little wave and guns it back towards the track. David Letterman used to do "A brush with greatness". This was a "Brush-back from Greatness"! The guy's pretty short in real life...
Jim N.
'73 Bahia Red 2.0
'84 Camaro Z28 HO (First new car)
'96 Kawasaki GPZ1100 (When you feel the need for real speed)
'81 Ducati 900SS Mike Hailwood (When you feel the need for a back ache)
Posted by: MattR Sep 29 2005, 02:28 AM
Very interesting stuff Jim.
Did you get the PM I sent you? I wasnt sure it was sent because the club site went down right after.
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